The tissues that compose and support joint surfaces are collectively called osteochondral tissues. The most superficial of these, the articular cartilage, is essential for absorbing shock and maintaining normal joint environment, and, regardless of the cause, degeneration of articular cartilage can result in irreversible osteoarthritis. While this loss of cartilage is the most noticeable affect of osteoarthritis there are also many changes to the underlying bone caused by injury and osteoarthritis. In degenerated joints there is a thickening, or sclerosis of the bone and frequently the formation of bone marrow lesions. Nutrition to these tissues is provided by the bone marrow and disruption of the tissues may also compromise nutrition causing further degeneration.
Debate continues as to the initial event(s) that causes osteoarthritis. Some investigators contend that articular cartilage changes precede subchondral bone changes; while other investigators contend the opposite. It appears that changes in articular cartilage and subchondral tissues are so intertwined that distinguishing a single initiating change in either tissue is difficult. However it is clear that any strategies for repair of cartilage defects or cartilage bone defects must account for changes to the bone.
A number of medical devices have been developed to facilitate the repair of osteo and osteochondral defects. These devices typically comprise cylindrical plugs that can be inserted into holes drilled perpendicular to, and through, the articular cartilage of the defect. The osteochondral plugs are often bi-phasic in design with each phase designed to regenerate either the articular cartilage tissue or the bone by aligning with that tissue in vivo. The devices are generally made from resorbable materials, and often comprise fibers dispersed in a second material.
U.S. Pat. No. 4,279,249 to Vert et al. discloses a non-porous osteosynthesis device made from biodegradable polymers that is reinforced with fibers. U.S. Pat. No. 5,306,311 to Stone et al. discloses a resorbable scaffold for articular cartilage regeneration comprising a porous matrix of randomly, circumferentially or radially oriented fibers such that the matrix has a surface contour substantially the same as natural articular cartilage. Preferably, at least some of the fibers are cross-linked. EP Patent No. 0,277,678 A1 to Leenslag et al. discloses grafts for use in reconstructive surgery that are matrices of organic polymeric materials incorporating degradable fibers having a bi-porous structure with each structure having its own pore size and pore size distribution. EP Patent No. 1,357,953 to Callegaro et al. discloses grafts for the repair of osteochondral defects wherein the grafts are constituted by a three-dimensional matrix of hyaluronic acid derivatives with a structure containing empty spaces; a porous, three-dimensional matrix constituted by a ceramic material; optionally containing pharmacologically or biologically active ingredients. U.S. Pat. No. 5,607,474 to Athanasiou et al. discloses multi-phase bioerodible implants for osteo and osteochondral defect repair. These implants include a first bioerodible polymeric material bonded to a second bioerodible polymeric material with each material having different mechanical properties. These biphasic porous implants are implanted such that the first material resides substantially within the bone of an osteochondral defect, and the second material resides substantially within the cartilage. Each material is selected and formed to permit tissue ingrowth in order to allow regeneration of bone and cartilage. U.S. Pat. No. 6,511,511 to Slivka et al. discloses fiber-reinforced polymeric implants that can be used for osteo and osteochondral repair, wherein the chopped fibers are aligned inside biodegradable porous matrices and the ratio of the volume of fibers to the biodegradable polymeric material is between 0.05 and about 0.5.
In order to further improve the repair of osteochondral defects, it is desirable to identify an implant that can allow good communication between the base of the defect (in the bone), and the cartilage surface. Ideally, the implant would permit cells that populate the bone marrow to migrate throughout the defect resulting in improved regeneration of both the bone and the cartilage. Furthermore, it is desirable for the repair to be deep enough to reach through the diseased and sclerotic bone tissue to the bone marrow, since nutrition is derived from the bone marrow deep below the cartilage surface.
It is therefore an object of the present invention to provide implants that will facilitate the regeneration of the tissue in osteo and osteochondral defects, and in ligament and tendon injuries.
It is further object of the invention to provide implants comprising a means such that when implanted the lower surfaces are situated in an area rich in bone marrow and the bone marrow can migrate through the implant.
It is still another object of the invention to provide methods for manufacturing biocompatible implants comprising fibers or braids coated with bioceramic, and methods of manufacture, to enhance osteointegration.
It is yet another object of the invention to provide methods for implanting the implants.